Directional radio beacon



Jam, W, CARL-ERIK GRANQVIST DIRECTIONAL RADIQ BEACON Filed Oct. 29, 19402 Sheets-Sheet l (005 Mama/10mm mafia/14177549 Jam. Wy W43 CARL-ERIKGRANQVIST mww DIRECTIONAL RADIO BEACON Filed Oct. 29, 1940 ZSheets-Sheet2 I I lmpzp/a/vce r W R IMP'OAM/CE 600E Mec/m/v/JM Max WENT? BY W2;

Patented Jan. 19, 1943 UN iTED PATENT OFFICE DIRECTIONAL RADIO BEACONApplication October 29, 1940, Serial No. 363,281 In Sweden April 10,1940 13 Claims.

My invention relates to directional radio beacons.

Directional radio beacons, are known, in which the direction oftransmission is periodically reversed, to form the code letters e and tor a and n or with other code letters. Hence a listener who is on oneside of a certain plane through the radio beacon will only hear theletter e (or a) whereas a listener on the other side of this plane willonly hear the letter t (11). If the listener is travelling from one sideof the radio beacon to the other he will pass a certain position, viz.the said plane, where he hears the signal e and the signal 1.simultaneously with equal intensity. As these signals were formed byshifting the direction of propagation of the beacon, the signals willcomplete each other, so that a continuous tone is heard.

These radio beacons are usually called E-T- beacons. The sharpness ofthe directional characteristic of this kind of beacon is relativelygood, but it has been found that for certain purposes a greatersharpness is desirable. This is the case when the beacons are arrangedas an aid for navigating in very narrow or difficult waters. The presentinvention relates to an arrangement by means of which the sharpness ofthe directional characteristic may be varied as desired. One specialadvantage of the invention is that the apparatus is very simple anddependable and the sharpness of the directional characteristic can bechanged by changing only one simple directing means, no change in theparts associated with the radio transmitter being required. Radiobeacons of a standard type may be used and the directional sharpness maybe varied as desired.

According to the invention dipole antennas are used. In the dipole planethere is applied as a director a screen of metal or other conductingmaterial, and the antenna is fed nonsymmetrically.

The invention is further described in connection with the annexeddrawings, in which Figs. 1, 2 and 3 show different diagrams inexplanation of the directional characteristics of dipoles, and Figs. 4-8show different forms of transmitters embodying the invention.

The field intensity diagram for a normal dipole antenna has the form ofthe letter 8. This is shown in Fig. l. The dipole contains the two halfparts ll and I2. The directional characteristic is indicated by thecurve l3. If a screen M, Fig. 2, of infinite extent is placed betweenthe inner ends of the dipoles and connected to ground the transmissiondiagram is changed into the diagram shown in Fig. 2, composed of fourloops. Between the two forms of the characteristic shown in Figs. 1 and2, viz. for a dipole antenna with screen of zero extension and ofinfinite extension, there is an innumerable number of intermediateforms, produced by different screens with various finite, predeterminedextensions. Fig. 3 shows such an arrangement together with thecharacteristics, obtained by the same. The invention is based upon theobservation that the angle l5, at which the characteristic crosses theplane through the screen, varies from when the screen has zero extension(Fig. 1) to 0, when the screen has infinite extension (Fig. 2), and thatthus any desired angle can be obtained by varying the extension of thescreen.

It is the steepness of the angle l5 which determines the sharpness ofthe directional characteristic in the plane of the screen. Hence bychoosing a screen of suitable magnitude the sharpness of the directionalcharacteristic may be varied as desired.

Fig. 4 shows perspectively an arrangement according to the presentinvention, partly in block diagram. The antenna in this arrangement isformed by dipole bars l6 and H, which are preferably made of pipes, andwhich are connected to the transmitter 3| by means of the conductors i8and IS. A contact device 20 is provided'at the connection point of theconductors l8 and I9 to the antenna bars [6 and IT, respectively. Thismay comprise a relay 2!, having a contact spring which makes contactwith a back-contact 22, when the relay is deenergized and with a frontcontact 23 when the relay 2! is energized.

The counter-contacts 22 and 23 are connectedcharacteristics 26 and 21for the antenna [6 andthe field characteristics 28 and 29 for theantenna IT, as shown in Fig. 3. Only one of these characteristics willbe transmitted if one of the bars is connected to ground through thescreen 25.

The transmission takes place as described,

above in time with an easily recognizable code, for instance the codeletters e and t, so that a listener on one side of the plane of thescreen M will hear only one of the letters, whereas a listener on theother side of this plane will hear only the other letter. A listenerlocated in this plane will however hear a continuous tone formed by bothof the code letters in such a way, that no interruption and no change ofthe sound intensity is present.

In practice it is impossible to so adjust the contacts of relay 2| thatno disturbances arise at the moment of switching over. The backcontact22 may be opened either after or before the front-contact 23 is closed.In both cases an audible click will be produced in the receivingapparatus. Such a click interferes with the observations and decreasesthe effectiveness of the very high theoretical sharpness of thedirectional characteristic.

This disadvantage is avoided according to one embodiment of the presentinvention by making the intensity of the transmitter such, that thecharacteristic when both of the dipole half parts are transmitting, isof the form shown by the dotted line curve 30 in Fig. 3. This can beobtained by a certain extension of the screen Hi. If the steepness ofthe curve and the sharpness of the directional characteristic which isobtained by this dimension of the screen i4 is sufiicient, it is obviousthat a directional transmitter is thus obtained having a highersharpness of its directional characteristics than those obtained byprevious arrangements of similar simplicity. If, on the other hand, therequirements for sharpness are such that the screen Ill must be of amagnitude at which freedom from audible switching click is not obtained,other steps must be taken for decreasing or avoiding the switchingclick. To a certain extent this can be attained by suitably choosing thelength of the dipole antennas. Other arrangements for this purpose arehown in Figs. 4 to 8.

In Fig. 4 two contacts are used for the change of transmission. Thiscan, however, also be produced by using only one contact, as shown inFig. 5. In this arrangement both of the dipole antenna parts areconnected in a bridge coupling together with two impedances 32 and 33,two adjacent bridge branches being formed by the capacities to ground ofthe dipole antenna parts and the screen, respectively, whereas the twoimpedances form the two remaining branches. The reference characters areotherwise the same as in Fig. 4. The impedances 32 and 33 are connectedto the screen, the impedance 33 directly and the impedance 32 through acontact 33, which is influenced by a relay 2i operated by a codemechanism 24. The impedances 32 and 33 are not equal, the impedance 33preferably being larger than the impedance 32. The dipole antenna I6 isthus rendered partly inactive when the contact 34 is closed, as theimpedance 32 is then acting as a short circuiting resistance, whereaswith the contact 33 open the impedance 33 causes an unbalance in such adirection that the antenna I! is partly short circuited. With thisarrangement the characteristics are not reduced to zero, but they changebetween two unequal values, so that one or the other is greaterdepending upon whether the contact 34 is open or closed. By suitablychoosing the impedances 32 and 33 symmetry may be obtained between thecharacteristics of the two dipole antenna parts.

' with the respective dipole antenna parts A clickless change over mayalso be obtained by a continuous switching system as shown in Figs. 6and 7.

In the arrangement according to Fig. 6 one of the impedances 32 has beenreplaced by a continuously variable condenser 42, which rotates andthereby continuously varies between a maximum value, corresponding tominimum of impedance, and a minimum value, corresponding to maximum ofimpedance. The condenser 42 is mechanically controlled by a codemechanism 43, and the movement of this may not be at constant speed, butthe speed may be varied in any suitable manner. It is especiallysuitable to use a pendulum movement or an oscillating movement,interrupted by shorter or longer periods of rest.

A more advantageous action is obtained by providing a difierentialcondenser as shown in Fig. 7. The rotor 35 of this condenser isconnected to the code mechanism, whereas the two stator parts 36 and 3!are fixed. The rotor is electrically connected to the screen 25, whereasthe stators 3G and 3'! are electrically connected it and H.

If an exceptional freedom from switching clicks is desired the changesof the load produced by the movement of the condenser may be compensatedfor by two symmetrical load compensation resistors 38 and 39 and acondenser 43 in a compensation circuit between the two stators 36 and31. The condenser 33 is mechanically controlled in accordance with themovement of the rotor 35, preferably by connecting the rotors of both ofthe condensers to the same shaft, but electrically isolated from eachother. Of course both of the resistors 33 and 39 may be replaced by onecommon resistance although a certain unsymmetry may be thus produced.

The system can of course be modified in various ways. If the directionaltransmitter is arranged at the end of a channel, for example, areflector may be used to eliminate the loops 2'! and 29 of thecharacteristic in Fig. 3, the loops 23 and 28 thereby being madecorrespondingly greater. One suitable method of accomplishing this is toarrange in the screen It a numberof metallic bars 4| as shown in Fig. 8.A metallic part of the transmitter itself, such as its chassis may beused as the screen if desired, to thereby obtain an easily transportableunit, containing the transmitter system as well as the antenna system.

What is claimed is:

1. A directional radio transmitter comprising a single dipole antennahaving two oppositely extending linear radiators, a generator of radiofrequency oscillations connected to feed said antenna, control meansalternately rendering said radiators inactive, and a reflector screenbetween said dipole antenna radiators in a plane perpendicular to saidradiators suited to alter the directional characteristics thereof.

2. A directional radio transmitter as set forth in claim 1 in which thecontrol means comprises means for alternately connecting said radiatorsto said screen.

3. A directional radio transmitter as set forth in claim 1 in which saidscreen is grounded and the control means comprises means for alternatelyconnecting said radiators to said screen.

4. A directional radio transmitter as set forth in claim 1 in which thecontrol means comprises a make and break contact connected toalternately connect said radiators to said screen.

5. A directional radio transmitter as set forth in claim 1 in which thecontrol means comprises a make and break contact connected toalternately connect said radiators to said screen, a relay connected toactuate said contact and code mechanism actuating said relay.

6. A directional radio transmitter as set forth in claim 1 in which theradiators are connected to said screen through impedances constituting,with the capacity of the radiators to ground, a bridge circuit and inwhich the control means Varies the value of one of said impedances sothat the radiators transmit alternately with different fieldintensities.

7. A directional radio transmitter as set forth in claim 1 in which theradiators are connected to said screen through impedances constituting,with the capacity of the radiators to ground, a bridge circuit and inwhich the control means comprises a contact connected to open and closeone of the branches of said bridge.

8. A directional radio transmitter as set forth in claim 1 in which theradiators are connected to said screen through impedances constituting,with the capacity of the radiators to ground, a bridge circuit and inwhich the control means varies the value of one of said impedances sothat the radiators transmit alternately different field intensities, oneof said impedances comprising a condenser which is continuously variablebetween a maximum and minimum value.

9. A directional radio transmitter as set forth in claim 1 in which theradiators are connected to said screen through impedances constituting,with the capacity of the radiators to ground, a

bridge circuit and in which the control means varies the value of one ofsaid impedances so that the radiators transmit alternately differentfield intensities, said impedances comprising a differential condenserhaving fixed plates connected to said radiators and a movable plateconnected to said screen to provide a continuously variable control forthe radiation characteristics of said radiators.

10. A directional radio transmitter as set forth in claim 1 in which theradiators are connected to said screen through impedances constituting,with the capacity of the radiators to ground, a bridge circuit and inwhich the control means varies the value of one of said impedances sothat the radiators transmit alternately different field intensities,said impedances comprising a difierential condenser having fixed platesconnected to said radiators and a movable plate connected to said screento provide a continuously variable control for the radiationcharacteristics of said radiators and a variable balance circuitcontaining symmetrically arranged resistances in series with a variablecondenser connected to said difierential plates, said condenser beingactuated in unison with aid first condenser in a manner to avoidirregularities in operation during the change-over periods.

11. A directional radio transmitter as set forth in claim 1 in which thereflector screen and the radiators are so related that the fieldintensity is substantially the same throughout the entire period ofoperation of the system.

12. A directional radio transmitter as set forth in claim 1 in which anadditional reflector is provided to direct the transmitted energy in asingle direction only.

13. A directional radio transmitter as set forth in claim 1 in which areflector is provided comprising a plurality of bars extendingsubstantially perpendicular to said screen and parallel with saidradiators, said reflector being adapted to confine the transmission to asingle direction only.

CARL-ERIK GRANQVIST.

